1. Field of the Disclosure
The present disclosure relates to a process for preparing titanium dioxide, and in particular to the in-situ formation of chlorides in the preparation of titanium dioxide.
2. Background of the Disclosure
Titanium dioxide pigments are prepared using either the chloride process or the sulfate process. In the preparation of titanium dioxide pigments by the vapor phase chloride process, titanium tetrachloride, TiCl4, is reacted with an oxygen containing gas at temperatures ranging from about 900° C. to about 1600° C., the resulting hot gaseous suspension of TiO2 particles and free chlorine is discharged from the reactor and must be quickly cooled below about 600° C., for example, by passing it through a conduit, i.e., flue, where growth of the titanium dioxide pigment particles and agglomeration of said particles takes place.
It is known to add various substances, such as silicon compounds and aluminum compounds, to the reactants in order to improve the pigmentary properties of the final product. Aluminum trichloride added during the process has been found to increase rutile in the final product, and silicon tetrachloride that becomes silica in the final product has been found to improve carbon black undertone (CBU), particle size and pigment abrasion. It is useful to be able to add elements to the titanium dioxide particles. However, the process and materials to be added to improve properties of the titanium dioxide particles may be hazardous.
A need exists for a low cost approach for adding elements to the process without the need for transportation of a highly toxic material, special processing equipment and expensive facilities. A need also exists for a process wherein the feed to the AlCl3 generator can be continuous with no shutdown required for maintenance on the equipment.